The present invention relates to a tracked vehicle drive/steering system.
Known production tracked vehicles, such as the John Deere 8000T and 9000T series track tractors, include an engine-driven variable displacement steering pump which powers a hydraulic fixed displacement steering motor. The steering motor drives, via a cross shaft and a gear, a left planetary drive. The steering motor also drives, via the cross shaft, a gear and a reverser gear, a right planetary drive. A steering control signal is provided by a transducer which detects rotation of a steering wheel. The speed and direction of rotation of the steering motor is normally proportional to the position of the steering wheel, and these parameters are sensed by a Hall effect motor speed and direction sensor. Certain types of steering pump related failures, such as contamination in the control valve and malfunction of the feedback linkage between the steering pump swashplate and its second stage control valves could cause the pump swashplate to hydraulically lock (stick) at a certain non-zero position. This type of failure can lead to a continuous turning of the vehicle, even when the steering wheel is in a position commanding no turn. It would be desirable to provide a method of detecting such failures, and of preventing vehicle turning unless turning is actually commanded by the operator.